[FFmpeg-user] Yes or No? About the processing pipeline.

[Mark Filipak]

On 18/06/2025 02.55, Paul B Mahol wrote:
> On Tue, Jun 17, 2025 at 11:19 PM Mark Filipak <

>> Maybe you can tell me why this experiment fails.
>>
>> ffmpeg^
>>    -i "c:\8-bit ybr420 smpte170m.mkv"^
>>    -map 0 -c:v libx264 -c:a copy^
>>    "c:\8-bit ybr420 smpte170m.mp4"

>> Input #0, matroska,webm, from 'c:\8-bit ybr420 smpte170m.mkv':
>>     Stream #0:0: Video: mpeg2video (Main), yuv420p(tv, smpte170m, progressive), 720x480 [SAR 32:27 DAR 16:9], 23.98 fps, 23.98 tbr, 1k tbn (default)
>>     Stream #0:1: Audio: ac3, 48000 Hz, 5.1(side), fltp, 448 kb/s, Start 0.004000 (default)
>>     Stream #0:2: Subtitle: dvd_subtitle (dvdsub), 720x480

>> [sost#0:2 @ 0000000004c5ec80] Automatic encoder selection failed Default
>> encoder for format mp4
>> (codec none) is probably disabled. Please choose an encoder manually.


> You need to select video encoder manually because it failed to pick one for
> you automatically.


Well, that's certainly what it says.

Apparently '-map 0' is no longer enough if you don't copy all streams.


This (map va, copy va) succeeds:

ffmpeg^
  -i "c:\8-bit ybr420 smpte170m.mkv"^
  -map 0:v -map 0:a -c:v libx264 -c:a copy^
  "c:\8-bit ybr420 smpte170m.mp4"


This (copy vas) succeeds:

ffmpeg^
  -i "c:\8-bit ybr420 smpte170m.mkv"^
  -map 0 -c:v libx264 -c:a copy -c:s copy^
  "c:\8-bit ybr420 smpte170m.mp4"


This (copy va) fails:

ffmpeg^
  -i "c:\8-bit ybr420 smpte170m.mkv"^
  -map 0 -c:v libx264 -c:a copy^
  "c:\8-bit ybr420 smpte170m.mp4"

It fails with a nonsense error message.