Re: [FFmpeg-devel] [PATCH] libavformat/hlsenc: add AVFMT_VARIABLE_FPS flag to mimic mpegtsenc

[Carl Eugen Hoyos]

2017-12-08 1:14 GMT+01:00 Aman Gupta :
> From: Aman Gupta 
>
> Previously, using a filter that changed frame_rate/time_base would work
> as expected with mpegtsenc, but duplicate frames when used with hlsenc
> (which uses mpegtsenc underneath).
>
> For instance, using https://tmm1.s3.amazonaws.com/720p.ts:
>
> $ ffmpeg -i 720p.ts -c:v libx264 -an -filter:v 
> "yadif=mode=send_field:deint=interlaced" -f mpegts -y single.ts
> $ ffmpeg -i 720p.ts -c:v libx264 -an -filter:v 
> "yadif=mode=send_field:deint=interlaced" -f hls -hls_time 30 -y segment.m3u8
>
> One would expect single.ts and segment0.ts to be identical, however comparing 
> them shows:
>
> single.ts:   120 fps,  59.94 tbr, 90k tbn, 239.76 tbc
> segment0.ts: 120 fps, 119.88 tbr, 90k tbn, 239.76 tbc
>
> Without AVFMT_VARIABLE_FPS set, ffmpeg.c was duplicating frames in the hlsenc
> case and generating segments with double the r_frame_rate.
>
> After this commit, the two muxers generate identical output.

But the mp4 muxer does not support variable frame rate output...

Carl Eugen
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[FFmpeg-devel] [PATCH] libavformat/hlsenc: add AVFMT_VARIABLE_FPS flag to mimic mpegtsenc

[Aman Gupta]

From: Aman Gupta 

Previously, using a filter that changed frame_rate/time_base would work
as expected with mpegtsenc, but duplicate frames when used with hlsenc
(which uses mpegtsenc underneath).

For instance, using https://tmm1.s3.amazonaws.com/720p.ts:

$ ffmpeg -i 720p.ts -c:v libx264 -an -filter:v 
"yadif=mode=send_field:deint=interlaced" -f mpegts -y single.ts
$ ffmpeg -i 720p.ts -c:v libx264 -an -filter:v 
"yadif=mode=send_field:deint=interlaced" -f hls -hls_time 30 -y segment.m3u8

One would expect single.ts and segment0.ts to be identical, however comparing 
them shows:

single.ts:   120 fps,  59.94 tbr, 90k tbn, 239.76 tbc
segment0.ts: 120 fps, 119.88 tbr, 90k tbn, 239.76 tbc

Without AVFMT_VARIABLE_FPS set, ffmpeg.c was duplicating frames in the hlsenc
case and generating segments with double the r_frame_rate.

After this commit, the two muxers generate identical output.
---
 libavformat/hlsenc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/libavformat/hlsenc.c b/libavformat/hlsenc.c
index 7dc8f4237b..d256498244 100644
--- a/libavformat/hlsenc.c
+++ b/libavformat/hlsenc.c
@@ -2335,7 +2335,7 @@ AVOutputFormat ff_hls_muxer = {
 .audio_codec= AV_CODEC_ID_AAC,
 .video_codec= AV_CODEC_ID_H264,
 .subtitle_codec = AV_CODEC_ID_WEBVTT,
-.flags  = AVFMT_NOFILE | AVFMT_GLOBALHEADER | AVFMT_ALLOW_FLUSH,
+.flags  = AVFMT_NOFILE | AVFMT_GLOBALHEADER | AVFMT_VARIABLE_FPS | 
AVFMT_ALLOW_FLUSH,
 .write_header   = hls_write_header,
 .write_packet   = hls_write_packet,
 .write_trailer  = hls_write_trailer,
-- 
2.14.2

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