Re: [FFmpeg-devel] [PATCH v3] avformat/nutdec: Don't create inconsistent side data

[Andreas Rheinhardt <andreas.rheinhardt@outlook.com>]

Michael Niedermayer:
> On Thu, May 30, 2024 at 07:53:42PM +0200, Andreas Rheinhardt wrote:
>> Michael Niedermayer:
>>> On Thu, May 30, 2024 at 02:14:20AM +0200, Andreas Rheinhardt wrote:
>>>> Forgotten in 65ddc74988245a01421a63c5cffa4d900c47117c.
>>>>
>>>> Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
>>>> ---
>>>>  libavformat/nutdec.c | 14 ++++----------
>>>>  1 file changed, 4 insertions(+), 10 deletions(-)
>>>>
>>>> diff --git a/libavformat/nutdec.c b/libavformat/nutdec.c
>>>> index 0bb7f154db..34b7e3cb9a 100644
>>>> --- a/libavformat/nutdec.c
>>>> +++ b/libavformat/nutdec.c
>>>> @@ -881,8 +881,6 @@ static int read_sm_data(AVFormatContext *s, AVIOContext *bc, AVPacket *pkt, int
>>>>      int count = ffio_read_varlen(bc);
>>>>      int skip_start = 0;
>>>>      int skip_end = 0;
>>>> -    int channels = 0;
>>>> -    int64_t channel_layout = 0;
>>>>      int sample_rate = 0;
>>>>      int width = 0;
>>>>      int height = 0;
>>>> @@ -930,7 +928,7 @@ static int read_sm_data(AVFormatContext *s, AVIOContext *bc, AVPacket *pkt, int
>>>>                  AV_WB64(dst, v64);
>>>>                  dst += 8;
>>>>              } else if (!strcmp(name, "ChannelLayout") && value_len == 8) {
>>>> -                channel_layout = avio_rl64(bc);
>>>> +                // Ignored
>>>>                  continue;
>>>>              } else {
>>>>                  av_log(s, AV_LOG_WARNING, "Unknown data %s / %s\n", name, type_str);
>>>> @@ -952,7 +950,7 @@ static int read_sm_data(AVFormatContext *s, AVIOContext *bc, AVPacket *pkt, int
>>>>              } else if (!strcmp(name, "SkipEnd")) {
>>>>                  skip_end = value;
>>>>              } else if (!strcmp(name, "Channels")) {
>>>> -                channels = value;
>>>> +                // Ignored
>>>>              } else if (!strcmp(name, "SampleRate")) {
>>>>                  sample_rate = value;
>>>>              } else if (!strcmp(name, "Width")) {
>>>> @@ -965,18 +963,14 @@ static int read_sm_data(AVFormatContext *s, AVIOContext *bc, AVPacket *pkt, int
>>>>          }
>>>>      }
>>>>  
>>>> -    if (channels || channel_layout || sample_rate || width || height) {
>>>> -        uint8_t *dst = av_packet_new_side_data(pkt, AV_PKT_DATA_PARAM_CHANGE, 28);
>>>> +    if (sample_rate || width || height) {
>>>> +        uint8_t *dst = av_packet_new_side_data(pkt, AV_PKT_DATA_PARAM_CHANGE, 16);
>>>>          if (!dst)
>>>>              return AVERROR(ENOMEM);
>>>>          bytestream_put_le32(&dst,
>>>>                              AV_SIDE_DATA_PARAM_CHANGE_SAMPLE_RATE*(!!sample_rate) +
>>>>                              AV_SIDE_DATA_PARAM_CHANGE_DIMENSIONS*(!!(width|height))
>>>>                             );
>>>> -        if (channels)
>>>> -            bytestream_put_le32(&dst, channels);
>>>> -        if (channel_layout)
>>>> -            bytestream_put_le64(&dst, channel_layout);
>>>>          if (sample_rate)
>>>>              bytestream_put_le32(&dst, sample_rate);
>>>>          if (width || height){
>>>
>>> This would break mid stream changes to the channel layout & channels when it
>>> is carried at format level only
>>>
>>> The commit message also does not adequately explain why such mid stream changes
>>> are ignored
>>>
>>
>> Mid-stream changes like this have been deprecated in
>> 09b5d3fb44ae1036700f80c8c80b15e9074c58c3;
>> 65ddc74988245a01421a63c5cffa4d900c47117c removed it, but only
>> incompletely: The side data flags for channel count and channel layout
>> changes were no longer written (in fact, they were removed from
>> packet.h), yet it still wrote the rest of the side data as if these
>> flags existed and had been written. That is the inconsistency this
>> commit addresses. It does not address whether channel count/layout
>> updates should have been removed, because that has already happened.
> 
> i honestly belive that we should support changing channel(layout) for
> cases like PCM in nut
> 

That is orthogonal to this patch (which just wants to not create
inconsistent side data).

- Andreas

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