ffmpeg: Add demuxer options. (#426)

This adds demuxer options as a complement to the existing encoder/muxer
options which allows us to:

1. explicitly select the demuxer to use if probing doesn't return a good result

2. configure the demuxer with additional options

This has come up a few times while looking at various things so it is good to
have an API that is fully configurable out of the box.

ffmpeg/decoder.c

@@ -355,10 +355,19 @@ int open_input(input_params *params, struct input_ctx *ctx)
 
   ctx->transmuxing = params->transmuxing;
 
-  // open demuxer/ open demuxer
+  const AVInputFormat *fmt = NULL;
+  if (params->demuxer.name) {
+    fmt = av_find_input_format(params->demuxer.name);
+    if (!fmt) {
+      ret = AVERROR_DEMUXER_NOT_FOUND;
+      LPMS_ERR(open_input_err, "Invalid demuxer name")
+    }
+  }
+
+  // open demuxer
   AVDictionary **demuxer_opts = NULL;
   if (params->demuxer.opts) demuxer_opts = &params->demuxer.opts;
-  ret = avformat_open_input(&ic, inp, NULL, demuxer_opts);
+  ret = avformat_open_input(&ic, inp, fmt, demuxer_opts);
   if (ret < 0) LPMS_ERR(open_input_err, "demuxer: Unable to open input");
   // If avformat_open_input replaced the options AVDictionary with options that were not found free it
   if (demuxer_opts) av_dict_free(demuxer_opts);

ffmpeg/ffmpeg.go

@@ -98,6 +98,7 @@ type TranscodeOptionsIn struct {
 	Device      string
 	Transmuxing bool
 	Profile     VideoProfile
+	Demuxer     ComponentOptions
 }
 
 type TranscodeOptions struct {
@@ -948,6 +949,12 @@ func (t *Transcoder) Transcode(input *TranscodeOptionsIn, ps []TranscodeOptions)
 
 	var demuxerOpts C.component_opts
 
+	if input.Demuxer.Name != "" {
+		demuxerName := C.CString(input.Demuxer.Name)
+		defer C.free(unsafe.Pointer(demuxerName))
+		demuxerOpts.name = demuxerName
+	}
+
 	ext := filepath.Ext(input.Fname)
 	// If the input has an image file extension setup the image2 demuxer
 	if ext == ".png" {
@@ -963,14 +970,17 @@ func (t *Transcoder) Transcode(input *TranscodeOptionsIn, ps []TranscodeOptions)
 				input.Profile.FramerateDen = 1
 			}
 
-			// Do not try to free in this function because in the C code avformat_open_input()
-			// will destroy this
-			demuxerOpts.opts = newAVOpts(map[string]string{
-				"framerate": fmt.Sprintf("%d/%d", input.Profile.Framerate, input.Profile.FramerateDen),
-			})
+			// changing the input map here is maybe not great
+			input.Demuxer.Opts["framerate"] = fmt.Sprintf("%d/%d", input.Profile.Framerate, input.Profile.FramerateDen)
 		}
 	}
 
+	if len(input.Demuxer.Opts) > 0 {
+		// Do not free in this function because avformat_open_input()
+		// in the C code will destroy this
+		demuxerOpts.opts = newAVOpts(input.Demuxer.Opts)
+	}
+
 	inp := &C.input_params{fname: fname, hw_type: hw_type, device: device, xcoderParams: xcoderParams,
 		handle: t.handle, demuxer: demuxerOpts}
 	if input.Transmuxing {

ffmpeg/ffmpeg_test.go

@@ -2377,3 +2377,65 @@ func runRotationTests(t *testing.T, accel Acceleration) {
 	`
 	run(cmd)
 }
+
+func TestTranscoder_DemuxerOpts(t *testing.T) {
+	// generate test files: a few frames of raw video
+	run, dir := setupTest(t)
+	defer os.RemoveAll(dir)
+
+	cmd := `
+		# use an unusual pixel format
+		ffmpeg -i "$1/../transcoder/test.ts" -an -c:v rawvideo -pix_fmt gbrp12be -s 320x240 -r 1 -frames:v 3 -f rawvideo test.raw
+		ffprobe -show_streams -count_frames -pixel_format gbrp12be -video_size 320x240 -f rawvideo test.raw 2>&1 | grep nb_read_frames=3
+	`
+	run(cmd)
+	res, err := Transcode3(
+		&TranscodeOptionsIn{
+			Fname: dir + "/test.raw",
+			Demuxer: ComponentOptions{
+				Name: "rawvideo",
+				Opts: map[string]string{
+					"fflags":       "+discardcorrupt+nobuffer",
+					"pixel_format": "gbrp12be",
+					"video_size":   "320x240",
+				},
+			},
+		},
+		[]TranscodeOptions{{
+			Oname: dir + "/out-%d.png",
+			Profile: VideoProfile{
+				Name:       "-",
+				Resolution: "200x150",
+				Bitrate:    "10k",
+			},
+		}})
+	assert.Nil(t, err, "transcoder returned error")
+	assert := assert.New(t)
+	// we transcode 3 but decode/encode 2 due to nobuffer
+	assert.Equal(2, res.Decoded.Frames, "decoded frame count did  not match")
+	assert.Equal(2, res.Encoded[0].Frames, "encoded frame count did not match")
+	assert.Equal(int64(2*320*240), res.Decoded.Pixels, "decoded pixel count did not match")
+	assert.Equal(int64(2*200*150), res.Encoded[0].Pixels, "encoded frame count did not match")
+}
+
+func TestTranscoder_DemuxerOptsError(t *testing.T) {
+
+	// nonexistent demuxer
+	_, err := Transcode3(&TranscodeOptionsIn{
+		Fname: "../transcoder/test.ts",
+		Demuxer: ComponentOptions{
+			Name: "nonexistent",
+		},
+	}, nil)
+	assert.Equal(t, "Demuxer not found", err.Error())
+
+	// wrong demuxer
+	_, err = Transcode3(&TranscodeOptionsIn{
+		Fname: "../transcoder/test.ts",
+		Demuxer: ComponentOptions{
+			Name: "mp4",
+		},
+	}, nil)
+	assert.Equal(t, "Invalid data found when processing input", err.Error())
+
+}

ffmpeg/transcoder.c

@@ -168,7 +168,15 @@ int transcode_init(struct transcode_thread *h, input_params *inp,
   if (!ictx->ic) {
     // reopen demuxer for the input segment if needed
     // XXX could open_input() be re-used here?
-    ret = avformat_open_input(&ictx->ic, inp->fname, NULL, demuxer_opts);
+    const AVInputFormat *fmt = NULL;
+    if (inp->demuxer.name) {
+      fmt = av_find_input_format(inp->demuxer.name);
+      if (!fmt) {
+        ret = AVERROR_DEMUXER_NOT_FOUND;
+        LPMS_ERR(transcode_cleanup, "Invalid demuxer name")
+      }
+    }
+    ret = avformat_open_input(&ictx->ic, inp->fname, fmt, demuxer_opts);
     if (ret < 0) LPMS_ERR(transcode_cleanup, "Unable to reopen demuxer");
     // If avformat_open_input replaced the options AVDictionary with options that were not found free it
     if (demuxer_opts) av_dict_free(demuxer_opts);