feat(telegram): split oversized videos into playable parts (#229)

* feat(telegram): split oversized videos losslessly

* fix(telegram): respect Premium upload limits

* fix(telegram): keep split videos in one album

config/storage/telegram.go

@@ -8,14 +8,16 @@ import (
 
 type TelegramStorageConfig struct {
 	BaseConfig
-	ChatID    int64 `toml:"chat_id" mapstructure:"chat_id" json:"chat_id"`
-	ForceFile bool  `toml:"force_file" mapstructure:"force_file" json:"force_file"`
-	RateLimit int   `toml:"rate_limit" mapstructure:"rate_limit" json:"rate_limit"`
-	RateBurst int   `toml:"rate_burst" mapstructure:"rate_burst" json:"rate_burst"`
-	SkipLarge bool  `toml:"skip_large" mapstructure:"skip_large" json:"skip_large"` // skip files larger than Telegram limit(2GB)
-	// split files larger than Telegram limit(2GB) into parts of specified size, in MB, leave 0 to set default(2000MB)
+	ChatID          int64 `toml:"chat_id" mapstructure:"chat_id" json:"chat_id"`
+	ForceFile       bool  `toml:"force_file" mapstructure:"force_file" json:"force_file"`
+	RateLimit       int   `toml:"rate_limit" mapstructure:"rate_limit" json:"rate_limit"`
+	RateBurst       int   `toml:"rate_burst" mapstructure:"rate_burst" json:"rate_burst"`
+	SkipLarge       bool  `toml:"skip_large" mapstructure:"skip_large" json:"skip_large"` // skip files larger than Telegram limit(2GB)
+	SplitLargeVideo bool  `toml:"split_large_video" mapstructure:"split_large_video" json:"split_large_video"`
+	// split files larger than the uploader account limit into parts of specified size, in MB
+	// leave 0 to use the account limit (2000MB for bots/regular users, 4000MB for Premium users)
 	// only effective when SkipLarge is false
-	// use zip when splitting
+	// use zip when splitting non-video files or when lossless video splitting is disabled/unavailable
 	SplitSizeMB int64 `toml:"split_size_mb" mapstructure:"split_size_mb" json:"split_size_mb"`
 }
 

core/tasks/tfile/caption_test.go

@@ -0,0 +1,42 @@
+package tfile
+
+import (
+	"testing"
+
+	"github.com/gotd/td/tg"
+	tfilepkg "github.com/krau/SaveAny-Bot/pkg/tfile"
+)
+
+func TestSourceCaption(t *testing.T) {
+	tests := []struct {
+		name string
+		file tfilepkg.TGFile
+		want string
+		ok   bool
+	}{
+		{
+			name: "original caption",
+			file: tfilepkg.NewTGFile(nil, nil, 0, "video.mov", tfilepkg.WithMessage(&tg.Message{Message: "original caption"})),
+			want: "original caption",
+			ok:   true,
+		},
+		{
+			name: "empty caption suppresses storage fallback",
+			file: tfilepkg.NewTGFile(nil, nil, 0, "video.mov", tfilepkg.WithMessage(&tg.Message{})),
+			ok:   true,
+		},
+		{
+			name: "file without source message",
+			file: tfilepkg.NewTGFile(nil, nil, 0, "video.mov"),
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, ok := sourceCaption(tt.file)
+			if ok != tt.ok || got != tt.want {
+				t.Fatalf("sourceCaption() = (%q, %v), want (%q, %v)", got, ok, tt.want, tt.ok)
+			}
+		})
+	}
+}

core/tasks/tfile/execute.go

@@ -12,6 +12,8 @@ import (
 	"github.com/krau/SaveAny-Bot/common/utils/fsutil"
 	"github.com/krau/SaveAny-Bot/config"
 	"github.com/krau/SaveAny-Bot/pkg/enums/ctxkey"
+	"github.com/krau/SaveAny-Bot/pkg/storagetypes"
+	tfilepkg "github.com/krau/SaveAny-Bot/pkg/tfile"
 )
 
 func (t *Task) Execute(ctx context.Context) error {
@@ -57,6 +59,9 @@ func (t *Task) Execute(ctx context.Context) error {
 		return fmt.Errorf("failed to get file stat: %w", err)
 	}
 	vctx := context.WithValue(ctx, ctxkey.ContentLength, fileStat.Size())
+	if caption, ok := sourceCaption(t.File); ok {
+		vctx = storagetypes.WithSourceCaption(vctx, caption)
+	}
 	err = retry.Retry(func() error {
 		file, err := os.Open(t.localPath)
 		if err != nil {
@@ -73,3 +78,11 @@ func (t *Task) Execute(ctx context.Context) error {
 	}
 	return nil
 }
+
+func sourceCaption(file tfilepkg.TGFile) (string, bool) {
+	messageFile, ok := file.(tfilepkg.TGFileMessage)
+	if !ok || messageFile.Message() == nil {
+		return "", false
+	}
+	return messageFile.Message().GetMessage(), true
+}

docs/content/en/deployment/configuration/storages.md

@@ -79,7 +79,8 @@ Stream mode is not supported.
 chat_id = "123456789" # Telegram chat ID, the bot will send files to this chat
 force_file = false # Force sending as file, default is false
 skip_large = false # Skip large files, default is false. If enabled, files exceeding Telegram's limit will not be uploaded.
-spilt_size_mb = 2000 # Split size in MB, default is 2000 MB (2 GB). Files larger than this will be split into multiple parts (zip format). Ignored when skip_large is true.
+split_large_video = false # Losslessly split oversized videos into one album of up to 10 independently playable parts. Falls back to ZIP parts on failure or when more than 10 parts are required.
+split_size_mb = 0 # Split size in MB. 0 uses the uploader account limit: 2000 MB for bots/regular users and 4000 MB for Premium users. Oversized non-video files use ZIP parts. Ignored when skip_large is true.
 ```
 
 ## Rclone

docs/content/zh/deployment/configuration/storages.md

@@ -82,10 +82,12 @@ chat_id = "123456789"
 force_file = false
 # 是否跳过大文件, 默认为 false. 如果启用, 超过 Telegram 限制的文件将不会上传.
 skip_large = false
-# 分卷大小, 单位 MB, 默认为 2000 MB (2 GB). 
-# 超过该大小的文件将被分割成多个部分上传.(使用 zip 格式)
+# 超限视频是否使用 FFmpeg 无损分割成一个媒体组（最多 10 个）内可独立播放的小视频；失败或需要超过 10 段时回退到 ZIP 分卷.
+split_large_video = false
+# 分卷大小, 单位 MB. 设为 0 时使用实际上传账号的限制：Bot/普通用户为 2000 MB，Premium 用户为 4000 MB.
+# 超过该大小的文件将被分割成多个部分上传；非视频使用 ZIP 格式.
 # 当 skip_large 启用时, 该选项无效.
-spilt_size_mb = 2000
+split_size_mb = 0
 ```
 
 ## Rclone

pkg/storagetypes/context.go

@@ -0,0 +1,19 @@
+package storagetypes
+
+import "context"
+
+type sourceCaptionContextKey struct{}
+
+// WithSourceCaption records the source Telegram message caption for storage
+// backends that can preserve it. Calling this function with an empty caption
+// intentionally suppresses a backend-generated fallback caption.
+func WithSourceCaption(ctx context.Context, caption string) context.Context {
+	return context.WithValue(ctx, sourceCaptionContextKey{}, caption)
+}
+
+// SourceCaptionFromContext returns the source caption and whether the caller
+// explicitly supplied one.
+func SourceCaptionFromContext(ctx context.Context) (string, bool) {
+	caption, ok := ctx.Value(sourceCaptionContextKey{}).(string)
+	return caption, ok
+}

pkg/storagetypes/context_test.go

@@ -0,0 +1,24 @@
+package storagetypes
+
+import (
+	"context"
+	"testing"
+)
+
+func TestSourceCaptionContext(t *testing.T) {
+	if _, ok := SourceCaptionFromContext(context.Background()); ok {
+		t.Fatal("caption unexpectedly present on empty context")
+	}
+
+	tests := []string{"original caption", ""}
+	for _, want := range tests {
+		ctx := WithSourceCaption(context.Background(), want)
+		got, ok := SourceCaptionFromContext(ctx)
+		if !ok {
+			t.Fatalf("caption %q was not marked as present", want)
+		}
+		if got != want {
+			t.Fatalf("caption = %q, want %q", got, want)
+		}
+	}
+}

storage/telegram/telegram.go

@@ -34,8 +34,9 @@ import (
 
 const (
 	// https://core.telegram.org/api/config#upload-max-fileparts-default
-	DefaultSplitSize  = 4000 * 524288 // 4000 * 512 KB
-	MaxUploadFileSize = 4000 * 524288 // 4000 * 512 KB
+	DefaultSplitSize         = 4000 * 524288 // 4000 * 512 KB
+	MaxUploadFileSize        = 4000 * 524288 // 4000 * 512 KB
+	PremiumMaxUploadFileSize = 8000 * 524288 // 8000 * 512 KB
 )
 
 type Telegram struct {
@@ -86,17 +87,21 @@ func (t *Telegram) Exists(ctx context.Context, storagePath string) bool {
 }
 
 func (t *Telegram) Save(ctx context.Context, r io.Reader, storagePath string) error {
+	storagePath = path.Clean(storagePath)
+	captionOverride := sourceCaptionOverride(ctx)
 	tctx := tgutil.ExtFromContext(ctx)
 	if tctx == nil {
 		return fmt.Errorf("failed to get telegram context")
 	}
 	size := contentLength(ctx)
-	if t.config.SkipLarge && size > MaxUploadFileSize {
-		log.FromContext(ctx).Warnf("Skipping file larger than Telegram limit (%d bytes): %d bytes", MaxUploadFileSize, size)
+	maxUploadSize := maxUploadFileSize(tctx)
+	if t.config.SkipLarge && size > maxUploadSize {
+		log.FromContext(ctx).Warnf("Skipping file larger than Telegram limit (%d bytes): %d bytes", maxUploadSize, size)
 		return nil
 	}
-	if size > t.splitSize() {
-		filename, chatID := t.target(tctx, path.Clean(storagePath))
+	splitSize := t.splitSize(maxUploadSize)
+	if size > splitSize {
+		filename, chatID := t.target(tctx, storagePath)
 		if filename == "" {
 			if rs, ok := r.(io.ReadSeeker); ok {
 				mtype, err := mimetype.DetectReader(rs)
@@ -117,7 +122,43 @@ func (t *Telegram) Save(ctx context.Context, r io.Reader, storagePath string) er
 		if err := t.limiter.Wait(ctx); err != nil {
 			return fmt.Errorf("rate limit failed: %w", err)
 		}
-		return t.splitUpload(tctx, r, filename, upler, peer, size, t.splitSize())
+		if t.config.SplitLargeVideo {
+			rs, ok := r.(io.ReadSeeker)
+			if ok {
+				mtype, detectErr := mimetype.DetectReader(rs)
+				if _, seekErr := rs.Seek(0, io.SeekStart); seekErr != nil {
+					return fmt.Errorf("failed to seek large file after mimetype detection: %w", seekErr)
+				}
+				if detectErr != nil {
+					log.FromContext(ctx).Warnf("Failed to detect large file type, falling back to ZIP split: %s", detectErr)
+				} else if strings.HasPrefix(mtype.String(), "video/") {
+					parts, cleanup, splitErr := createLosslessVideoParts(
+						ctx,
+						rs,
+						filename,
+						size,
+						splitSize,
+					)
+					if splitErr != nil {
+						if ctx.Err() != nil {
+							return ctx.Err()
+						}
+						log.FromContext(ctx).Warnf("Lossless video split failed, falling back to ZIP split: %s", splitErr)
+					} else {
+						defer cleanup()
+						log.FromContext(ctx).Infof("Uploading oversized video as %d lossless-playable parts", len(parts))
+						for _, part := range parts {
+							log.FromContext(ctx).Infof("Prepared lossless video part %s (%d bytes)", part.Name, part.Size)
+						}
+						return t.uploadLosslessVideoParts(ctx, tctx, storagePath, parts, captionOverride)
+					}
+					if _, seekErr := rs.Seek(0, io.SeekStart); seekErr != nil {
+						return fmt.Errorf("failed to seek large video before ZIP fallback: %w", seekErr)
+					}
+				}
+			}
+		}
+		return t.splitUpload(tctx, r, filename, upler, peer, size, splitSize)
 	}
 
 	if err := t.limiter.Wait(ctx); err != nil {
@@ -143,12 +184,27 @@ func contentLength(ctx context.Context) int64 {
 	return -1
 }
 
-func (t *Telegram) splitSize() int64 {
+func sourceCaptionOverride(ctx context.Context) *string {
+	caption, ok := storagetypes.SourceCaptionFromContext(ctx)
+	if !ok {
+		return nil
+	}
+	return &caption
+}
+
+func maxUploadFileSize(tctx *ext.Context) int64 {
+	if tctx != nil && tctx.Self != nil && !tctx.Self.GetBot() && tctx.Self.GetPremium() {
+		return PremiumMaxUploadFileSize
+	}
+	return MaxUploadFileSize
+}
+
+func (t *Telegram) splitSize(maxUploadSize int64) int64 {
 	splitSize := t.config.SplitSizeMB * 1024 * 1024
 	if splitSize <= 0 {
-		return DefaultSplitSize
+		return maxUploadSize
 	}
-	return splitSize
+	return min(splitSize, maxUploadSize)
 }
 
 func (t *Telegram) target(tctx *ext.Context, storagePath string) (string, int64) {
@@ -310,7 +366,9 @@ func (t *Telegram) SaveBatch(ctx context.Context, items []storagetypes.BatchItem
 func (t *Telegram) inspectBatchItem(tctx *ext.Context, item storagetypes.BatchItem) (batchMediaItem, error) {
 	_, chatID := t.target(tctx, path.Clean(item.StoragePath))
 	result := batchMediaItem{item: item, chatID: chatID}
-	if (t.config.SkipLarge && item.Size > MaxUploadFileSize) || item.Size > t.splitSize() {
+	maxUploadSize := maxUploadFileSize(tctx)
+	if (t.config.SkipLarge && item.Size > maxUploadSize) ||
+		item.Size > t.splitSize(maxUploadSize) {
 		result.useSingleSave = true
 		return result, nil
 	}
@@ -362,6 +420,9 @@ func (t *Telegram) saveMediaGroup(ctx context.Context, tctx *ext.Context, group
 				return fmt.Errorf("failed to seek batch item: %w", err)
 			}
 			itemCtx := context.WithValue(ctx, ctxkey.ContentLength, item.Size)
+			if item.PreserveCaption {
+				itemCtx = storagetypes.WithSourceCaption(itemCtx, item.Caption)
+			}
 			return t.Save(itemCtx, item.Reader, item.StoragePath)
 		}
 		if err := t.limiter.Wait(ctx); err != nil {

storage/telegram/upload_limit_test.go

@@ -0,0 +1,119 @@
+package telegram
+
+import (
+	"bytes"
+	"testing"
+
+	"github.com/celestix/gotgproto/ext"
+	"github.com/gotd/td/tg"
+	"github.com/krau/SaveAny-Bot/pkg/storagetypes"
+)
+
+func TestMaxUploadFileSize(t *testing.T) {
+	tests := []struct {
+		name string
+		ctx  *ext.Context
+		want int64
+	}{
+		{name: "missing context", want: MaxUploadFileSize},
+		{name: "missing self", ctx: new(ext.Context), want: MaxUploadFileSize},
+		{
+			name: "bot",
+			ctx:  uploadAccountContext(true, false),
+			want: MaxUploadFileSize,
+		},
+		{
+			name: "premium bot still uses bot limit",
+			ctx:  uploadAccountContext(true, true),
+			want: MaxUploadFileSize,
+		},
+		{
+			name: "regular user",
+			ctx:  uploadAccountContext(false, false),
+			want: MaxUploadFileSize,
+		},
+		{
+			name: "premium user",
+			ctx:  uploadAccountContext(false, true),
+			want: PremiumMaxUploadFileSize,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := maxUploadFileSize(tt.ctx); got != tt.want {
+				t.Fatalf("maxUploadFileSize() = %d, want %d", got, tt.want)
+			}
+		})
+	}
+}
+
+func uploadAccountContext(bot, premium bool) *ext.Context {
+	self := new(tg.User)
+	self.SetBot(bot)
+	self.SetPremium(premium)
+	return &ext.Context{Self: self}
+}
+
+func TestSplitSizeUsesUploaderLimit(t *testing.T) {
+	tests := []struct {
+		name         string
+		splitSizeMB  int64
+		accountLimit int64
+		want         int64
+	}{
+		{
+			name:         "bot default",
+			accountLimit: MaxUploadFileSize,
+			want:         MaxUploadFileSize,
+		},
+		{
+			name:         "premium default",
+			accountLimit: PremiumMaxUploadFileSize,
+			want:         PremiumMaxUploadFileSize,
+		},
+		{
+			name:         "explicit lower limit",
+			splitSizeMB:  1500,
+			accountLimit: PremiumMaxUploadFileSize,
+			want:         1500 * 1024 * 1024,
+		},
+		{
+			name:         "explicit limit is capped by account",
+			splitSizeMB:  5000,
+			accountLimit: PremiumMaxUploadFileSize,
+			want:         PremiumMaxUploadFileSize,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			telegramStorage := Telegram{}
+			telegramStorage.config.SplitSizeMB = tt.splitSizeMB
+			if got := telegramStorage.splitSize(tt.accountLimit); got != tt.want {
+				t.Fatalf("splitSize() = %d, want %d", got, tt.want)
+			}
+		})
+	}
+}
+
+func TestBatchUploadLimitAppliesPerFile(t *testing.T) {
+	telegramStorage := Telegram{}
+	tctx := uploadAccountContext(true, false)
+	data := []byte("\x00\x00\x00\x18ftypmp42\x00\x00\x00\x00mp42isom")
+	itemSize := int64(MaxUploadFileSize/2 + 1)
+
+	for index := 0; index < 2; index++ {
+		item, err := telegramStorage.inspectBatchItem(tctx, storagetypes.BatchItem{
+			Reader:      bytes.NewReader(data),
+			StoragePath: "video.mp4",
+			Size:        itemSize,
+		})
+		if err != nil {
+			t.Fatalf("inspectBatchItem() failed for item %d: %v", index, err)
+		}
+		if item.useSingleSave {
+			t.Fatalf("item %d was treated as oversized even though only the batch total exceeds the limit", index)
+		}
+	}
+}

storage/telegram/video_split.go

@@ -0,0 +1,358 @@
+package telegram
+
+import (
+	"context"
+	"fmt"
+	"io"
+	"math"
+	"os"
+	"os/exec"
+	"path"
+	"path/filepath"
+	"sort"
+	"strconv"
+	"strings"
+
+	"github.com/celestix/gotgproto/ext"
+	"github.com/charmbracelet/log"
+	"github.com/gotd/td/telegram/message"
+	"github.com/rs/xid"
+
+	"github.com/krau/SaveAny-Bot/config"
+)
+
+const (
+	videoPartTargetRatio  = 0.95
+	videoSplitAttempts    = 4
+	minSegmentDuration    = 1.0
+	maxLosslessVideoParts = 10
+)
+
+type losslessVideoPart struct {
+	Path string
+	Name string
+	Size int64
+}
+
+type mediaToolRunner func(ctx context.Context, name string, args ...string) ([]byte, error)
+
+var runMediaTool mediaToolRunner = func(ctx context.Context, name string, args ...string) ([]byte, error) {
+	cmd := exec.CommandContext(ctx, name, args...)
+	output, err := cmd.CombinedOutput()
+	if err != nil {
+		message := strings.TrimSpace(string(output))
+		if message == "" {
+			return nil, err
+		}
+		return nil, fmt.Errorf("%w: %s", err, message)
+	}
+	return output, nil
+}
+
+func createLosslessVideoParts(
+	ctx context.Context,
+	r io.ReadSeeker,
+	filename string,
+	fileSize, maxPartSize int64,
+) ([]losslessVideoPart, func(), error) {
+	inputPath, sourceCleanup, err := sourceFile(r)
+	if err != nil {
+		return nil, func() {}, fmt.Errorf("failed to prepare seekable video source: %w", err)
+	}
+
+	tempBase := config.C().Temp.BasePath
+	if err := os.MkdirAll(tempBase, 0o755); err != nil {
+		sourceCleanup()
+		return nil, func() {}, fmt.Errorf("failed to create video split base directory: %w", err)
+	}
+	tempDir, err := os.MkdirTemp(tempBase, "telegram-video-split-*")
+	if err != nil {
+		sourceCleanup()
+		return nil, func() {}, fmt.Errorf("failed to create video split directory: %w", err)
+	}
+	cleanup := func() {
+		if err := os.RemoveAll(tempDir); err != nil {
+			log.FromContext(ctx).Warnf("Failed to clean lossless video parts: %s", err)
+		}
+		sourceCleanup()
+	}
+
+	parts, err := splitLosslessVideo(ctx, inputPath, tempDir, filename, fileSize, maxPartSize)
+	if err != nil {
+		cleanup()
+		return nil, func() {}, err
+	}
+	return parts, cleanup, nil
+}
+
+func splitLosslessVideo(
+	ctx context.Context,
+	inputPath, outputDir, filename string,
+	fileSize, maxPartSize int64,
+) ([]losslessVideoPart, error) {
+	if fileSize <= maxPartSize {
+		return nil, fmt.Errorf("video size %d does not exceed part limit %d", fileSize, maxPartSize)
+	}
+	if maxPartSize <= 0 {
+		return nil, fmt.Errorf("invalid video part limit: %d", maxPartSize)
+	}
+
+	duration, err := probeMediaDuration(ctx, inputPath)
+	if err != nil {
+		return nil, fmt.Errorf("failed to probe source video duration: %w", err)
+	}
+	if duration < minSegmentDuration {
+		return nil, fmt.Errorf("invalid source video duration: %.3f", duration)
+	}
+
+	targetSize := int64(float64(maxPartSize) * videoPartTargetRatio)
+	segmentDuration := initialSegmentDuration(duration, fileSize, targetSize)
+	extension := videoPartExtension(filename)
+	outputPattern := filepath.Join(outputDir, "part-%03d"+extension)
+
+	var lastOversize int64
+	for attempt := 0; attempt < videoSplitAttempts; attempt++ {
+		if err := clearVideoParts(outputDir); err != nil {
+			return nil, err
+		}
+		if err := runFFmpegSegment(ctx, inputPath, outputPattern, extension, segmentDuration); err != nil {
+			return nil, fmt.Errorf("failed to losslessly split video: %w", err)
+		}
+
+		parts, largest, err := collectVideoParts(ctx, outputDir, filename)
+		if err != nil {
+			return nil, err
+		}
+		if len(parts) < 2 {
+			return nil, fmt.Errorf("video split produced %d part(s), expected at least 2", len(parts))
+		}
+		if len(parts) > maxLosslessVideoParts {
+			return nil, fmt.Errorf(
+				"video split produced %d parts, exceeding the single-album limit of %d",
+				len(parts),
+				maxLosslessVideoParts,
+			)
+		}
+		if largest <= maxPartSize {
+			return parts, nil
+		}
+
+		lastOversize = largest
+		segmentDuration *= float64(targetSize) / float64(largest)
+		if segmentDuration < minSegmentDuration {
+			break
+		}
+	}
+
+	return nil, fmt.Errorf(
+		"unable to keep lossless video parts below %d bytes; largest part was %d bytes",
+		maxPartSize,
+		lastOversize,
+	)
+}
+
+func initialSegmentDuration(duration float64, fileSize, targetSize int64) float64 {
+	partCount := math.Ceil(float64(fileSize) / float64(targetSize))
+	if partCount < 2 {
+		partCount = 2
+	}
+	segmentDuration := duration / partCount
+	if segmentDuration < minSegmentDuration {
+		return minSegmentDuration
+	}
+	return segmentDuration
+}
+
+func videoPartExtension(filename string) string {
+	extension := strings.ToLower(filepath.Ext(filepath.Base(filename)))
+	switch extension {
+	case ".avi", ".m4v", ".mkv", ".mov", ".mp4", ".ts", ".webm":
+		return extension
+	default:
+		return ".mp4"
+	}
+}
+
+func runFFmpegSegment(
+	ctx context.Context,
+	inputPath, outputPattern, extension string,
+	segmentDuration float64,
+) error {
+	args := []string{
+		"-hide_banner",
+		"-loglevel", "error",
+		"-nostdin",
+		"-y",
+		"-i", inputPath,
+		"-map", "0",
+		"-map_metadata", "0",
+		"-c", "copy",
+		"-f", "segment",
+		"-segment_time", strconv.FormatFloat(segmentDuration, 'f', 3, 64),
+		"-segment_start_number", "1",
+		"-reset_timestamps", "1",
+		"-avoid_negative_ts", "make_zero",
+	}
+	if extension == ".mp4" || extension == ".m4v" || extension == ".mov" {
+		args = append(args, "-segment_format_options", "movflags=+faststart")
+	}
+	args = append(args, outputPattern)
+	_, err := runMediaTool(ctx, "ffmpeg", args...)
+	return err
+}
+
+func probeMediaDuration(ctx context.Context, filePath string) (float64, error) {
+	output, err := runMediaTool(
+		ctx,
+		"ffprobe",
+		"-v", "error",
+		"-show_entries", "format=duration",
+		"-of", "default=noprint_wrappers=1:nokey=1",
+		filePath,
+	)
+	if err != nil {
+		return 0, err
+	}
+	duration, err := strconv.ParseFloat(strings.TrimSpace(string(output)), 64)
+	if err != nil {
+		return 0, fmt.Errorf("invalid ffprobe duration %q: %w", strings.TrimSpace(string(output)), err)
+	}
+	return duration, nil
+}
+
+func clearVideoParts(outputDir string) error {
+	entries, err := os.ReadDir(outputDir)
+	if err != nil {
+		return fmt.Errorf("failed to read video split directory: %w", err)
+	}
+	for _, entry := range entries {
+		if entry.IsDir() {
+			continue
+		}
+		if err := os.Remove(filepath.Join(outputDir, entry.Name())); err != nil {
+			return fmt.Errorf("failed to clear old video part %s: %w", entry.Name(), err)
+		}
+	}
+	return nil
+}
+
+func collectVideoParts(
+	ctx context.Context,
+	outputDir, filename string,
+) ([]losslessVideoPart, int64, error) {
+	matches, err := filepath.Glob(filepath.Join(outputDir, "part-*"))
+	if err != nil {
+		return nil, 0, fmt.Errorf("failed to list video parts: %w", err)
+	}
+	sort.Strings(matches)
+	if len(matches) == 0 {
+		return nil, 0, fmt.Errorf("ffmpeg did not produce any video parts")
+	}
+
+	extension := videoPartExtension(filename)
+	base := strings.TrimSuffix(filepath.Base(filename), filepath.Ext(filepath.Base(filename)))
+	if base == "" || base == "." {
+		base = xid.New().String()
+	}
+	parts := make([]losslessVideoPart, 0, len(matches))
+	var largest int64
+	for index, match := range matches {
+		info, err := os.Stat(match)
+		if err != nil {
+			return nil, 0, fmt.Errorf("failed to stat video part %s: %w", match, err)
+		}
+		if info.Size() <= 0 {
+			return nil, 0, fmt.Errorf("video part %s is empty", match)
+		}
+		if _, err := probeMediaDuration(ctx, match); err != nil {
+			return nil, 0, fmt.Errorf("failed to validate video part %s: %w", match, err)
+		}
+		if info.Size() > largest {
+			largest = info.Size()
+		}
+		parts = append(parts, losslessVideoPart{
+			Path: match,
+			Name: fmt.Sprintf("%s.part%03d%s", base, index+1, extension),
+			Size: info.Size(),
+		})
+	}
+	return parts, largest, nil
+}
+
+func partStoragePath(storagePath, partName string) string {
+	directory := path.Dir(path.Clean(storagePath))
+	if directory == "." || directory == "/" {
+		return partName
+	}
+	return path.Join(directory, partName)
+}
+
+func (t *Telegram) uploadLosslessVideoParts(
+	ctx context.Context,
+	tctx *ext.Context,
+	storagePath string,
+	parts []losslessVideoPart,
+	sourceCaption *string,
+) error {
+	if len(parts) == 0 {
+		return fmt.Errorf("no lossless video parts to upload")
+	}
+	if len(parts) > maxLosslessVideoParts {
+		return fmt.Errorf(
+			"refusing to upload %d lossless video parts as multiple albums; maximum is %d",
+			len(parts),
+			maxLosslessVideoParts,
+		)
+	}
+
+	prepared := make([]preparedMedia, 0, len(parts))
+	for index, part := range parts {
+		partFile, err := os.Open(part.Path)
+		if err != nil {
+			return fmt.Errorf("failed to open video part %s: %w", part.Name, err)
+		}
+		media, prepareErr := t.prepareMedia(
+			ctx,
+			tctx,
+			partFile,
+			partStoragePath(storagePath, part.Name),
+			part.Size,
+			videoPartCaption(sourceCaption, index),
+		)
+		closeErr := partFile.Close()
+		if prepareErr != nil {
+			return fmt.Errorf("failed to prepare video part %s: %w", part.Name, prepareErr)
+		}
+		if closeErr != nil {
+			return fmt.Errorf("failed to close video part %s: %w", part.Name, closeErr)
+		}
+		prepared = append(prepared, *media)
+	}
+
+	builder := tctx.Sender.WithUploader(prepared[0].uploader).To(prepared[0].peer)
+	if len(prepared) == 1 {
+		if _, err := builder.Media(ctx, prepared[0].media); err != nil {
+			return fmt.Errorf("failed to send video part: %w", err)
+		}
+		return nil
+	}
+	media := make([]message.MultiMediaOption, len(prepared))
+	for index := range prepared {
+		media[index] = prepared[index].media
+	}
+	if _, err := builder.Album(ctx, media[0], media[1:]...); err != nil {
+		return fmt.Errorf("failed to send video parts as album: %w", err)
+	}
+	return nil
+}
+
+func videoPartCaption(sourceCaption *string, index int) *string {
+	if sourceCaption == nil {
+		return nil
+	}
+	if index == 0 {
+		return sourceCaption
+	}
+	empty := ""
+	return &empty
+}

storage/telegram/video_split_test.go

@@ -0,0 +1,174 @@
+package telegram
+
+import (
+	"context"
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+func TestInitialSegmentDuration(t *testing.T) {
+	tests := []struct {
+		name       string
+		duration   float64
+		fileSize   int64
+		targetSize int64
+		want       float64
+	}{
+		{name: "two balanced parts", duration: 120, fileSize: 2200, targetSize: 1900, want: 60},
+		{name: "three balanced parts", duration: 120, fileSize: 3900, targetSize: 1900, want: 40},
+		{name: "minimum one second", duration: 1.5, fileSize: 3900, targetSize: 1900, want: 1},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := initialSegmentDuration(tt.duration, tt.fileSize, tt.targetSize)
+			if got != tt.want {
+				t.Fatalf("initialSegmentDuration() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}
+
+func TestVideoPartExtension(t *testing.T) {
+	tests := map[string]string{
+		"clip.MOV": ".mov",
+		"clip.mkv": ".mkv",
+		"clip.exe": ".mp4",
+		"clip":     ".mp4",
+	}
+	for input, want := range tests {
+		if got := videoPartExtension(input); got != want {
+			t.Fatalf("videoPartExtension(%q) = %q, want %q", input, got, want)
+		}
+	}
+}
+
+func TestPartStoragePath(t *testing.T) {
+	tests := map[string]string{
+		"clip.mov":            "clip.part001.mov",
+		"123456/clip.mov":     "123456/clip.part001.mov",
+		"/123456/clip.mov":    "/123456/clip.part001.mov",
+		"folder/sub/clip.mov": "folder/sub/clip.part001.mov",
+	}
+	for input, want := range tests {
+		if got := partStoragePath(input, "clip.part001.mov"); got != want {
+			t.Fatalf("partStoragePath(%q) = %q, want %q", input, got, want)
+		}
+	}
+}
+
+func TestVideoPartCaption(t *testing.T) {
+	if got := videoPartCaption(nil, 0); got != nil {
+		t.Fatalf("caption without source = %q, want nil", *got)
+	}
+
+	source := "original caption"
+	first := videoPartCaption(&source, 0)
+	if first == nil || *first != source {
+		t.Fatalf("first part caption = %v, want %q", first, source)
+	}
+	second := videoPartCaption(&source, 1)
+	if second == nil || *second != "" {
+		t.Fatalf("second part caption = %v, want an explicit empty caption", second)
+	}
+}
+
+func TestSplitLosslessVideoRetriesOversizedPart(t *testing.T) {
+	tempDir := t.TempDir()
+	inputPath := filepath.Join(tempDir, "source.mov")
+	if err := os.WriteFile(inputPath, []byte("source"), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	outputDir := filepath.Join(tempDir, "parts")
+	if err := os.Mkdir(outputDir, 0o755); err != nil {
+		t.Fatal(err)
+	}
+
+	originalRunner := runMediaTool
+	t.Cleanup(func() { runMediaTool = originalRunner })
+	ffmpegCalls := 0
+	runMediaTool = func(ctx context.Context, name string, args ...string) ([]byte, error) {
+		switch name {
+		case "ffprobe":
+			return []byte("120.0\n"), nil
+		case "ffmpeg":
+			ffmpegCalls++
+			pattern := args[len(args)-1]
+			sizes := []int{2001, 199}
+			if ffmpegCalls > 1 {
+				sizes = []int{1100, 1100}
+			}
+			for index, size := range sizes {
+				partPath := strings.Replace(pattern, "%03d", fmt.Sprintf("%03d", index+1), 1)
+				if err := os.WriteFile(partPath, make([]byte, size), 0o600); err != nil {
+					return nil, err
+				}
+			}
+			return nil, nil
+		default:
+			return nil, fmt.Errorf("unexpected media tool %q", name)
+		}
+	}
+
+	parts, err := splitLosslessVideo(t.Context(), inputPath, outputDir, "example.mov", 2200, 2000)
+	if err != nil {
+		t.Fatalf("splitLosslessVideo() failed: %v", err)
+	}
+	if ffmpegCalls != 2 {
+		t.Fatalf("ffmpeg calls = %d, want 2", ffmpegCalls)
+	}
+	if len(parts) != 2 {
+		t.Fatalf("parts = %d, want 2", len(parts))
+	}
+	if parts[0].Name != "example.part001.mov" || parts[1].Name != "example.part002.mov" {
+		t.Fatalf("unexpected part names: %#v", parts)
+	}
+	for _, part := range parts {
+		if part.Size > 2000 {
+			t.Fatalf("part %s exceeds limit: %d", part.Name, part.Size)
+		}
+	}
+}
+
+func TestSplitLosslessVideoRejectsMultipleAlbums(t *testing.T) {
+	tempDir := t.TempDir()
+	inputPath := filepath.Join(tempDir, "source.mov")
+	if err := os.WriteFile(inputPath, []byte("source"), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	outputDir := filepath.Join(tempDir, "parts")
+	if err := os.Mkdir(outputDir, 0o755); err != nil {
+		t.Fatal(err)
+	}
+
+	originalRunner := runMediaTool
+	t.Cleanup(func() { runMediaTool = originalRunner })
+	runMediaTool = func(ctx context.Context, name string, args ...string) ([]byte, error) {
+		switch name {
+		case "ffprobe":
+			return []byte("120.0\n"), nil
+		case "ffmpeg":
+			pattern := args[len(args)-1]
+			for index := 0; index < maxLosslessVideoParts+1; index++ {
+				partPath := strings.Replace(pattern, "%03d", fmt.Sprintf("%03d", index+1), 1)
+				if err := os.WriteFile(partPath, make([]byte, 100), 0o600); err != nil {
+					return nil, err
+				}
+			}
+			return nil, nil
+		default:
+			return nil, fmt.Errorf("unexpected media tool %q", name)
+		}
+	}
+
+	_, err := splitLosslessVideo(t.Context(), inputPath, outputDir, "example.mov", 2200, 2000)
+	if err == nil {
+		t.Fatal("splitLosslessVideo() succeeded with more than one album of parts")
+	}
+	if !strings.Contains(err.Error(), "single-album limit") {
+		t.Fatalf("splitLosslessVideo() error = %q, want single-album limit", err)
+	}
+}