[FFmpeg-devel] [PATCH] avformat/aiffenc: add aiff_init()

[James Almer]

On 6/17/2017 6:43 AM, Paul B Mahol wrote:
> On 5/28/17, James Almer <jamrial at gmail.com> wrote:
>> Signed-off-by: James Almer <jamrial at gmail.com>
>> ---
>>  libavformat/aiffenc.c | 45 +++++++++++++++++++++++++++++----------------
>>  1 file changed, 29 insertions(+), 16 deletions(-)
>>
>> diff --git a/libavformat/aiffenc.c b/libavformat/aiffenc.c
>> index fcadf149a0..1e0c5b11a0 100644
>> --- a/libavformat/aiffenc.c
>> +++ b/libavformat/aiffenc.c
>> @@ -98,13 +98,11 @@ static void put_meta(AVFormatContext *s, const char
>> *key, uint32_t id)
>>      }
>>  }
>>
>> -static int aiff_write_header(AVFormatContext *s)
>> +static int aiff_init(AVFormatContext *s)
>>  {
>>      AIFFOutputContext *aiff = s->priv_data;
>> -    AVIOContext *pb = s->pb;
>>      AVCodecParameters *par;
>> -    uint64_t sample_rate;
>> -    int i, aifc = 0;
>> +    int i;
>>
>>      aiff->audio_stream_idx = -1;
>>      for (i = 0; i < s->nb_streams; i++) {
>> @@ -126,6 +124,32 @@ static int aiff_write_header(AVFormatContext *s)
>>      /* First verify if format is ok */
>>      if (!par->codec_tag)
>>          return -1;
>> +
>> +    if (!par->bits_per_coded_sample)
>> +        par->bits_per_coded_sample = av_get_bits_per_sample(par->codec_id);
>> +    if (!par->bits_per_coded_sample) {
>> +        av_log(s, AV_LOG_ERROR, "could not compute bits per sample\n");
>> +        return -1;
>> +    }
>> +    if (!par->block_align)
>> +        par->block_align = (par->bits_per_coded_sample * par->channels) >>
>> 3;
>> +
>> +    avpriv_set_pts_info(s->streams[aiff->audio_stream_idx], 64, 1,
>> +
>> s->streams[aiff->audio_stream_idx]->codecpar->sample_rate);
>> +
>> +    return 0;
>> +}
>> +
>> +static int aiff_write_header(AVFormatContext *s)
>> +{
>> +    AIFFOutputContext *aiff = s->priv_data;
>> +    AVIOContext *pb = s->pb;
>> +    AVCodecParameters *par;
>> +    uint64_t sample_rate;
>> +    int aifc = 0;
>> +
>> +    par = s->streams[aiff->audio_stream_idx]->codecpar;
>> +
>>      if (par->codec_tag != MKTAG('N','O','N','E'))
>>          aifc = 1;
>>
>> @@ -165,15 +189,6 @@ static int aiff_write_header(AVFormatContext *s)
>>      aiff->frames = avio_tell(pb);
>>      avio_wb32(pb, 0);              /* Number of frames */
>>
>> -    if (!par->bits_per_coded_sample)
>> -        par->bits_per_coded_sample = av_get_bits_per_sample(par->codec_id);
>> -    if (!par->bits_per_coded_sample) {
>> -        av_log(s, AV_LOG_ERROR, "could not compute bits per sample\n");
>> -        return -1;
>> -    }
>> -    if (!par->block_align)
>> -        par->block_align = (par->bits_per_coded_sample * par->channels) >>
>> 3;
>> -
>>      avio_wb16(pb, par->bits_per_coded_sample); /* Sample size */
>>
>>      sample_rate = av_double2int(par->sample_rate);
>> @@ -199,9 +214,6 @@ static int aiff_write_header(AVFormatContext *s)
>>      avio_wb32(pb, 0);                    /* Data offset */
>>      avio_wb32(pb, 0);                    /* Block-size (block align) */
>>
>> -    avpriv_set_pts_info(s->streams[aiff->audio_stream_idx], 64, 1,
>> -
>> s->streams[aiff->audio_stream_idx]->codecpar->sample_rate);
>> -
>>      /* Data is starting here */
>>      avio_flush(pb);
>>
>> @@ -327,6 +339,7 @@ AVOutputFormat ff_aiff_muxer = {
>>      .priv_data_size    = sizeof(AIFFOutputContext),
>>      .audio_codec       = AV_CODEC_ID_PCM_S16BE,
>>      .video_codec       = AV_CODEC_ID_PNG,
>> +    .init              = aiff_init,
>>      .write_header      = aiff_write_header,
>>      .write_packet      = aiff_write_packet,
>>      .write_trailer     = aiff_write_trailer,
>> --
>> 2.12.1
>>
>> _______________________________________________
>> ffmpeg-devel mailing list
>> ffmpeg-devel at ffmpeg.org
>> http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
>>
> 
> Could you explain in detail what this patch does?

This, as well as the previous patch and every other patch that i haven't
yet sent, adds the missing init() function to the muxers so that
initialization is complete without the need to call write_header().
In this specific case, this is achieved by calling
avpriv_set_pts_info(), setting missing AVCodecParameters values and
doing some basic checks in init() instead of in write_header().

With this, calls to avformat_init_output() will return 1 (init complete)
rather than 0 (write_header needed) on most if not all muxers.
The idea is that, eventually, avformat_init_output() will become more
useful and used in ffmpeg.c rather than having it implicitly called from
within avformat_write_header(), to potentially simplify the code in that
file.

Is it useful and will help ffmpeg.c? I don't know, but it's worth a try.
Besides, it's proper to fully initialize the muxer in AVFormat.init()
when possible.