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POConvert MPEG4 to MPEGTS on Android with FFmpeg
 

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  1. POConvert MPEG4 to MPEGTS on Android with FFmpeg
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    <p>Ok, so obviously I know very little to none about ffmpeg API when I made the original post... it is quite overwhelming when one starts learning about digital media and conversion details. After reading quite a bit more and going through ffmpeg source, I was able to get a working output from mp4 to mpegts. The concept is similar to executing:</p> <pre><code>ffmpeg -i in.mp4 -vcodec copy -acodec copy -vbsf h264_mp4toannexb out.ts </code></pre> <p>But as I mentioned before, I need to implement it with ffmpeg API in C.</p> <p>So, although I am able to generate a playable .ts file, its video and audio streams are not synced. That is, playing them back on Android tablet plays the video very slowly while audio is playing at normal speed and then (once audio stream ends) video plays at normal speed to the end. Playing the same generated .ts file in VLC produces a very condensed audio (as though fast-forwarded) and plays video fine.</p> <p>There are still many aspects of media conversion that I am not familiar with. I am sure that some of them prevent me from successful conversion.</p> <p>Here is some information (via ffprobe) about the files: - in.mp4 - file generated via Android recording - MPEG4 (H.264 + AAC) - ffmpeg.ts - file generated via ffmpeg conversion - MPEG2TS (H.264 + AAC) - out.ts - file generated via my code - MPEGTS (H.264 + AAC)</p> <p><strong>in.mp4</strong> </p> <pre><code>filename=in.mp4 nb_streams=2 format_name=mov,mp4,m4a,3gp,3g2,mj2 format_long_name=QuickTime/MPEG-4/Motion JPEG 2000 format start_time=0:00:00.000000 duration=0:00:09.961383 size=4.730 Mibyte bit_rate=3.983 Mbit/s TAG:major_brand=isom TAG:minor_version=0 TAG:compatible_brands=isom3gp4 TAG:creation_time=2013-05-28 17:06:57 </code></pre> <p><strong>ffmpeg.ts</strong> </p> <pre><code>filename=ffmpeg.ts nb_streams=2 format_name=mpegts format_long_name=MPEG-2 transport stream format start_time=0:00:01.400000 duration=0:00:09.741267 size=5.132 Mibyte bit_rate=4.419 Mbit/s </code></pre> <p><strong>out.ts</strong> </p> <pre><code>filename=out.ts nb_streams=2 format_name=mpegts format_long_name=MPEG-2 transport stream format start_time=0:00:00.000000 duration=0:00:09.741267 size=5.166 Mibyte bit_rate=4.449 Mbit/s </code></pre> <p>Firstly, I was unable to affect my output file's start_time. Next, upon examining the -show_packets output of probe, I saw the following:</p> <p><strong>ffmpeg.ts</strong> </p> <pre><code>[PACKET] codec_type=video stream_index=0 pts=N/A pts_time=N/A dts=N/A dts_time=N/A duration=0 duration_time=0:00:00.000000 size=20.506 Kibyte pos=564 flags=K [/PACKET] [PACKET] codec_type=video stream_index=0 pts=N/A pts_time=N/A dts=N/A dts_time=N/A duration=0 duration_time=0:00:00.000000 size=11.727 Kibyte pos=22936 flags=_ [/PACKET] ... [PACKET] codec_type=audio stream_index=1 pts=126000 pts_time=0:00:01.400000 dts=126000 dts_time=0:00:01.400000 duration=2089 duration_time=0:00:00.023211 size=285.000 byte pos=109416 flags=K [/PACKET] [PACKET] codec_type=audio stream_index=1 pts=128089 pts_time=0:00:01.423211 dts=128089 dts_time=0:00:01.423211 duration=2089 duration_time=0:00:00.023211 size=374.000 byte pos=-1 flags=K [/PACKET] ... [PACKET] codec_type=video stream_index=0 pts=N/A pts_time=N/A dts=N/A dts_time=N/A duration=0 duration_time=0:00:00.000000 size=20.000 Kibyte pos=87232 flags=_ [/PACKET] [PACKET] codec_type=video stream_index=0 pts=N/A pts_time=N/A dts=N/A dts_time=N/A duration=0 duration_time=0:00:00.000000 size=16.852 Kibyte pos=112800 flags=_ [/PACKET] </code></pre> <p><strong>out.ts</strong></p> <pre><code>[PACKET] codec_type=audio stream_index=1 pts=0 pts_time=0:00:00.000000 dts=0 dts_time=0:00:00.000000 duration=2089 duration_time=0:00:00.023211 size=285.000 byte pos=22936 flags=K [/PACKET] [PACKET] codec_type=audio stream_index=1 pts=1024 pts_time=0:00:00.011378 dts=1024 dts_time=0:00:00.011378 duration=2089 duration_time=0:00:00.023211 size=374.000 byte pos=23312 flags=K [/PACKET] ... [PACKET] codec_type=video stream_index=0 pts=N/A pts_time=N/A dts=N/A dts_time=N/A duration=0 duration_time=0:00:00.000000 size=11.727 Kibyte pos=25004 flags=_ [/PACKET] [PACKET] codec_type=audio stream_index=1 pts=7168 pts_time=0:00:00.079644 dts=7168 dts_time=0:00:00.079644 duration=2089 duration_time=0:00:00.023211 size=299.000 byte pos=55460 flags=K [/PACKET] </code></pre> <p>As you can see, ffmpeg.ts starts out with video packets that do not have pts/dts. The audio packets that follow contain pts/dts. This repeats until the end. All video packets do not have pts/dts according to ffprobe output.</p> <p>However, out.ts starts with audio packets and alternate with video packets. Here, video packets also do not have pts/dts. The difference is that here there is one video packet between a series of audio packets. What happened to the rest of the video packets (ffmpeg.ts has ~5 audio followed by ~5 video).</p> <p>Obviously, I'm still learning and don't know way too much yet... Does anything jump out as obvious a problem to anyone? I will greatly appreciate any info / suggestions but will continue to grind at it!!</p>
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